HELP. My mac pro has had a kernel attack on startup

Sounds like a RAM problem.

Take out the one bad one and its pair and see if the problem stops.

You need the original install DVDs to rune Apple hardware test on older Macs

Using Apple Hardware Test

This tells you what slots are paired. The 2008 is near the bottom

Mac Pro (Mid 2012 and earlier): How to remove or install memory - Apple Support

If you can boot the Mac then go to Apple icon in upper right right and click on About this Mac. Then system report or profile depending upon OSX version. Then click on memory in left part and it will show installed memory and OK if it passed test..

Also if you open side cover during boot up are any diagnostic LEDs lit?

http://mediawiki.middlebury.edu/wiki/LIS/Apple_Diagnostic_Lights

The Macs runs fine with the side cover removed. It may get a littler warmer with uses since airflow is different

This;

one of the sticks of RAM sometimes doesn't register leaving me with 14gb of RAM. I just kept it in there.

Is bad. Can result in the old "GIGO" - garbage. Better to not run with the pair. And best to test with just new set, even one pair at a time.

FBDIMMs that don't work some of the time, do not work at all.

Try sliding out all the drives. When resetting SMC, with everything unplugged and disconnected (and remove 3rd party PCIe) hit power button also while unplugged.

Try different non-Apple kb and mouse too.

Get in the habit of always have a clean reliable system clone on hand for maintenance of any type, and an older working clone - in fact make a new clone before ever installing or applying any type of updates or changes.

Tried SAFE BOOT? Did you save and make a flash type installer for Yosemite or older? Always save those .ESD installer packages.

AHT does not find issues with GPUs or most RAM issues, the RAM issues it finds will show as errors, parity errors, in system profile already.

If it is not on 1500VA 900W UPS, that should be on your list of things to do and help protect it. And a smaller UPS maybe for routers and modems and disk drives or other external peripherals.

A set of FBDIMMs - 667's run cooler and cost much less - are $23 2x2GB on Amazon.

Your problem does not sound like a kernel panic or a memory problem to me.

If you get the gray Apple, then a progress Bar, that indicates your Boot Drive could not be mounted and it is being looked at with Disk Utility (Repair Disk [directory]). It never gets more than about a third of the way across, then the repair is complete.

a) If the disk was repaired enough to Mount, Startup will proceed.

b) If the disk still will not mount, your Mac is shut down under program control, since you can't do anything and its just going to get hot.

You need to Repair that drive, or substitute a different drive.

You need a running version of Mac OS X or Installer/Utilities on Recovery_HD or an the 10.6 DVD, or on a different drive.

Are you using a keyboard plugged directly into a USB on the chassis, not on a Display or other Hub?

Those others come up too late for the "snag keys" to work.

If you are getting the progress Bar, it is trying to boot normally. This could happen if your Drive is really, really sick, but is more likely an issue with not holding the keys soon enough.

You could try holding down Option from power on until you get the Startup Manager screen, then selecting the Recovery_HD.

For a wired keyboard, you should hold down Option or Command-R even before you power up. (The timing for a wireless keyboard requires you to wait until the chime is ending.)

If none of this gets you anywhere you will need another drive with a System on it that can boot your Mac Pro 2008 model. The 10.6 Installer/Utilities DVD is such a system, as is any thumb drive Installer/Utilities drive you may have made along the way.

With this much trouble, you should be thinking seriously about a replacement Hard Drive as well.